#snail shells

Above: the photo at the top shows a mason bee building its nest, while the illustration at the bottom shows the nest's internal structure

Bees of the family Megachilidae typically build their nests in the gaps and crevices in tree stumps, rocks, plant stems, and wooden structures, but there are a few species that prefer to nest in discarded snail shells. Most of these shell-nesting bees are found in Europe, North Africa, and the Near East; a few can also be found in North America, South Africa, and Japan.

Above: just some cozy little mason bees, Hoplitis zandeni and Osmia rufohirta

These are solitary bees, meaning that they don't form colonies or live together in hives, so each female builds her own individual nest. The nest is constructed as a series of brood cells, and each cell contains a single egg with enough pollen and nectar to sustain the larva until it reaches adulthood.

Shell-nesting mason bees are known to exist in at least five different genera, including Osmia, Hoplitis, Rhodanthidium, Wainia, and Protosmia.

Above: Osmia spinulosa and Rhodanthidium septemdentatum

When the female is ready to nest, she carefully selects a shell and then drags it into a shaded or well-hidden spot. Moving the shell is no easy feat, but she clings to it with her hind legs and pulls herself along by grabbing objects with her mandibles. A single bee may travel like that for several meters before finally settling on the right spot to prepare her nest.

Above: Osmia rufohirta dragging her shell into position

This article describes how the nest is then constructed:

The bee begins to build its nest, mainly within the “whorl” or spire of the shell. A typical nest consists of a few chambers (about two or four in number, depending on the size of the shell) known as cells, the walls of which consist of masticated leaf pulp known as leaf mastic. When fresh, the colour of this material is bright green, but with time, it assumes a brownish or black colour. Each cell is provisioned with a mixture of pollen and nectar, an egg is laid on this, and the cell sealed with further leaf mastic.

Above: two nests with their internal structures partially exposed, revealing the brood cells, larvae, pollen, nectar, and several layers of debris

The layout of the nest varies depending on the species, with some bees producing brood cells that are arranged into rows, while others create clustered or overlapping cells.

Above: the nest of a gold-fringed mason bee, Osmia aurulenta

The female must make dozens of trips just to gather the provisions for a single brood cell, and completing the entire nest can take days.

Once the brood chambers have been constructed and provisioned, the entrance to the shell is "bricked up" with several layers of plant pulp, soil, pebbles, and shell fragments. In some cases, the female will also apply patches of plant pulp to the outer surface of the shell as a way to provide camouflage.

Above: Oamia bicolor and Osmia aurulenta sealing their nests with plant pulp

The completed nest is then carefully maneuvered so that the entrance faces the ground. Some females will conceal the nest beneath a pile of twigs, pine needles, and plant stems, weaving moss and blades of grass throughout the pile. All of the debris is carefully selected, positioned, and then "glued" together with saliva, forming a tangled, tent-like structure over the nest.

Above: Osmia bicolor, commonly known as the red-tailed mason bee. constructing a protective thatch over her nest

In other cases, the female will conceal the nest by creating a small hole in the sand and then dragging the shell into it, ensuring that the nest is partially buried.

Above: Osmia aurulenta and Osmia rufohirta

This is just one of the many peculiar nesting habits that can be found among solitary bees. Several other examples have been featured in my previous posts, which describe the nest-building strategies of woolcarder bees, resin-pot bees, and a ground-dwelling species known as Osmia avosetta.

Above: the fully-constructed nest of a gold-fringed mason bee

Sources & More Info:

Bulletin of the Amateur Entomologists' Society: Shell-Nesting Bees

The Little Book of Bees: Snail-Nesting Mason Bees

University of Hradec Králové: Bees Nesting in Empty Gastropod Shells

Bees of the World: Snail Shells

The Wildlife Trusts: Red-Tailed Mason Bees

Insects: Nesting Preferences of Osmia orientalis

Journal of Hymenoptera Research: Comparative Biology of Four Rhodanthidium Species that Nest in Snail Shells

Journal of Hymenoptera Research: Biology of Palaearctic Wainia Bees of the Subgenus Caposmia

Cambridge University Press: The Native Shell-Nesting Bee Osmia conjuncta

Zootaxa: Palaearctic Osmia Bees of the Subgenera Hemiosmia, Tergosmia and Erythrosmia

I made this in a special spot I regularly walk through on my morning dog walks. It's inaccessible in the height of summer due to the nettles. Which I kind of love! I love that my practice must adapt to the world around me, that I must honour the seasons and the rhythms of nature.

For now, though, it's a regular stop on my daily walk. A place for contemplation, gratitude, offerings, and generally connecting to the earth.

Other pictures from snake road.